1. Field of the Invention
The present invention relates to a mirror angle control system for use in disc apparatuses, optical communication systems, and the like.
2. Description of Related Art
Conventionally, mirror angle control systems are used for the purposes of, among others, controlling tracking in disc apparatuses and controlling optical signal switches in optical communication systems.
For example, according to JP-A-2004-212205, a rotary mirror has a deflecting mirror surface and a detection reflective surface formed on the obverse and reverse sides of a rotatable plate-shaped member. Laser light from a light source is shone on the detection reflective surface, and the light reflected therefrom is received with a photoreceptor. Then, based on the position of the spot formed as a result on the photoreceptive surface of the photoreceptor, the inclination angle of the detection reflective surface is detected. Then, the inclination angle thus detected is converted into an equivalent deflection angle of the deflecting mirror surface. Then, based on the difference of this actually calculated deflection angle from the target deflection angle, the rotary mirror is controlled with an actuator on a feedback basis.
On the other hand, according to JP-A-2003-77154, a coil folder built as a movable member has a deflection mirror and a detection mirror fitted on the observe and reverse sides thereof. Laser light from a light source is shone on the detection mirror, and the light reflected therefrom is received with a photoreceptor. Then, based on the position of the spot formed as a result on the photoreceptive surface of the photoreceptor, the inclination angle of the detection mirror, hence the inclination angle of the deflection mirror, is detected. Then, based on the thus detected angle, the inclination angle of the deflection mirror is adjusted.
Disadvantageously, however, the mirror angle control systems disclosed in the patent publications mentioned above both require a detection mirror separate from a deflection mirror, and, depending on the accuracy with which these mirrors are fitted relative to each other, an error may be involved in the control of the inclination angle of the deflection mirror. As a result, a fault may occur in whatever product incorporates one of those control systems, for example, in the control of tracking in a disc apparatus or in the control of optical switching in an optical communication system.
Also disadvantageously, these control systems require, separate from a light source for shining laser light on a deflection mirror, another light source for shining laser light on a detection mirror. This makes it difficult to miniaturize products that incorporate the control systems, and also leads to increased electric power consumption.